The Experts below are selected from a list of 159 Experts worldwide ranked by ideXlab platform
Gordon D. Holman - One of the best experts on this subject based on the ideXlab platform.
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The Effects of Low‐ and High‐Energy Cutoffs on Solar Flare Microwave and Hard X‐Ray Spectra
The Astrophysical Journal, 2003Co-Authors: Gordon D. HolmanAbstract:Microwave and hard X-Ray Spectra provide crucial information about energetic electrons and their environment in solar flares. Both microwave and hard X-Ray Spectra are sensitive to cutoffs in the electron distribution function. The determination of the high-energy cutoff from these Spectra establishes the highest electron energies produced by the acceleration mechanism, while determination of the low-energy cutoff is crucial to establishing the total energy in accelerated electrons. I present computations of the effects of both high- and low-energy cutoffs on microwave and hard X-Ray Spectra. The optically thick portion of a microwave spectrum is enhanced and smoothed by a low-energy cutoff, while a hard X-Ray spectrum is flattened below the cutoff energy. A high-energy cutoff steepens the microwave spectrum and increases the wavelength at which the spectrum peaks, while the hard X-Ray spectrum begins to steepen at photon energies an order of magnitude or more below the electron cutoff energy. I discuss how flare microwave and hard X-Ray Spectra can be analyzed together to determine these electron cutoff energies.
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the effects of low and high energy cutoffs on solar flare microwave and hard X Ray Spectra
The Astrophysical Journal, 2003Co-Authors: Gordon D. HolmanAbstract:Microwave and hard X-Ray Spectra provide crucial information about energetic electrons and their environment in solar flares. Both microwave and hard X-Ray Spectra are sensitive to cutoffs in the electron distribution function. The determination of the high-energy cutoff from these Spectra establishes the highest electron energies produced by the acceleration mechanism, while determination of the low-energy cutoff is crucial to establishing the total energy in accelerated electrons. I present computations of the effects of both high- and low-energy cutoffs on microwave and hard X-Ray Spectra. The optically thick portion of a microwave spectrum is enhanced and smoothed by a low-energy cutoff, while a hard X-Ray spectrum is flattened below the cutoff energy. A high-energy cutoff steepens the microwave spectrum and increases the wavelength at which the spectrum peaks, while the hard X-Ray spectrum begins to steepen at photon energies an order of magnitude or more below the electron cutoff energy. I discuss how flare microwave and hard X-Ray Spectra can be analyzed together to determine these electron cutoff energies.
Martin Caon - One of the best experts on this subject based on the ideXlab platform.
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Off-aXis X-Ray Spectra: a comparison of Monte Carlo simulated and computed X-Ray Spectra with measured Spectra.
Medical physics, 1999Co-Authors: Madhava Bhat, John E. Pattison, Giovanni Bibbo, Martin CaonAbstract:The off-aXis X-Ray Spectra from a constant potential X-Raygenerator were measured with a high purity germaniumspectrometer cooled to liquid nitrogen temperature. The measuredSpectra were compared with off-aXis X-Ray Spectra calculated using a code based on the semiempirical model developed by Tucker et al. and Monte Carlo simulated X-Ray Spectra using the EGS4 code system. In this study, both the Tucker model, and the EGS4 code system, were found to produce off-aXis bremsstrahlung X-Ray Spectra which agreed well with the Spectrameasured at three emerging angles. In the measured and the EGS4generatedSpectra the total K-characteristic peaks were in increasing order, as observed in the anode to cathode direction, whereas the Tucker model produced maXimum total K-characteristic peaks at the 6° anode side, and lesser amounts at the central aXis and the 6° cathode side. Large differences in the total K-characteristic lines is seen among the three different methods. The EGS4 code system was able to produce X-Ray Spectra for a combination of target materials.
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Diagnostic X‐Ray Spectra: A comparison of Spectra generated by different computational methods with a measured spectrum
Medical physics, 1998Co-Authors: Madhava Bhat, John E. Pattison, Giovanni Bibbo, Martin CaonAbstract:A number of computer codes, developed using semi-empirical models, are available to compute X-Ray Spectra from a tungsten target for different tube parameters. In this study X-Ray Spectra measured with a high-purity germanium detector are compared with those computed using the empirical models and previously published measured data. The computer codes used to generate the Spectra are based on models proposed by Birch et al. and Tucker et al. The measured X-Ray Spectra agreed well with the computed X-Ray Spectra using the model of Tucker et al. whereas the model of Birch et al. produced a “harder” X-Ray spectrum compared to the measured Spectra. Our measured X-Ray Spectra compared well with the previously published measured Spectral data of Fewell et al.
Guy S. Miller - One of the best experts on this subject based on the ideXlab platform.
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X-Ray Spectra of Z Sources
The Astrophysical Journal, 1995Co-Authors: Dimitrios Psaltis, Frederick K. Lamb, Guy S. MillerAbstract:A physically consistent model has been proposed that seeks to eXplain in a unified way the X-Ray Spectra and rapid variability of the Z sources and other weakly magnetic neutron stars in low-mass systems. Here we describe a simple, four-parameter Spectral model derived from the unified model that accurately reproduces the X-Ray colors, Spectra, and count rates of the Z sources. In this model, photons are produced primarily by electron cyclotron emission in the neutron star magnetosphere and are then Comptonized in the magnetosphere, hot central corona, and inward radial flow. In addition to eXplaining their Z tracks, the model eXplains several other previously uneXplained properties of the Z sources.
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X-Ray Spectra of Z Sources
The Astrophysical Journal, 1995Co-Authors: Dimitrios Psaltis, Frederick K. Lamb, Guy S. MillerAbstract:A simple, physically consistent model has been proposed that seeks to eXplain in a unified way the X-Ray Spectra and rapid X-Ray variability of the so-called Z sources and other accreting neutron stars in low-mass systems. Here we summarize the results of detailed numerical calculations of the X-Ray Spectra of the Z sources predicted by this model. Our computations show that in the Z sources, photons are produced primarily by electron cyclotron emission in the neutron star magnetosphere. Comptonization of these photons by the hot central corona and radial inflow produces X-Ray Spectra, color-color tracks, and countrate variations like those observed in the Z sources.
K. Mukai - One of the best experts on this subject based on the ideXlab platform.
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The X-Ray Spectra of VY Scl Stars Are Not Blackbodies
The Astrophysical Journal, 2002Co-Authors: C. W. Mauche, K. MukaiAbstract:Using ASCA data, we find, contrary to other researchers using ROSAT data, that the X-Ray Spectra of the VY Scl stars TT Ari and KR Aur are poorly fit by an absorbed blackbody model but are well fit by an absorbed thermal plasma model. The different conclusions about the nature of the X-Ray spectrum of KR Aur may be due to differences in the accretion rate, since this star was in a high optical state during the ROSAT observation, but in an intermediate optical state during the ASCA observation. TT Ari, on the other hand, was in a high optical state during both observations, so directly contradicts the hypothesis that the X-Ray Spectra of VY Scl stars in their high optical states are blackbodies. Instead, based on theoretical eXpectations and the ASCA, Chandra, and XMM Spectra of other nonmagnetic cataclysmic variables, we believe that the X-Ray Spectra of VY Scl stars in their low and high optical states are due to hot thermal plasma in the boundary layer between the accretion disk and the surface of the white dwarf, and appeal to the acquisition of Chandra and XMM grating Spectra to test this prediction.
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X-Ray Spectra of VY Scl Stars Are Not Blackbodies
2001Co-Authors: C. W. Mauche, K. MukaiAbstract:Using ASCA data, we find, contrary to other researchers using ROSAT data, that the X, Ray Spectra of the VY Scl stars TT Ari and KR Aur are poorly fit by an absorbed blackbody model but are well fit by an absorbed thermal plasma model. The different conclusions about the nature of the X-Ray spectrum of KR Aur may be due to differences in the accretion rate, since this star was in a high optical state during the ROSAT observation, but in an intermediate optical state during the ASCA observation. TT Ari, on the other hand, was in a high optical state during both observations, so directly contradicts the hypothesis that the X-Ray Spectra of VY Sol stars in their high optical states are blackbodies. Instead, based on theoretical eXpectations and the ASCA, Chandra, and XMM Spectra of other nonmagnetic cataclysmic variables, we believe that the X-Ray Spectra of VY Sol stars in their low and high optical states are due to hot thermal plasma in the boundary layer between the accretion disk and the surface of the white dwarf, and appeal to the acquisition of Chandra and XMM grating Spectra to test this prediction.
Madhava Bhat - One of the best experts on this subject based on the ideXlab platform.
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Off-aXis X-Ray Spectra: a comparison of Monte Carlo simulated and computed X-Ray Spectra with measured Spectra.
Medical physics, 1999Co-Authors: Madhava Bhat, John E. Pattison, Giovanni Bibbo, Martin CaonAbstract:The off-aXis X-Ray Spectra from a constant potential X-Raygenerator were measured with a high purity germaniumspectrometer cooled to liquid nitrogen temperature. The measuredSpectra were compared with off-aXis X-Ray Spectra calculated using a code based on the semiempirical model developed by Tucker et al. and Monte Carlo simulated X-Ray Spectra using the EGS4 code system. In this study, both the Tucker model, and the EGS4 code system, were found to produce off-aXis bremsstrahlung X-Ray Spectra which agreed well with the Spectrameasured at three emerging angles. In the measured and the EGS4generatedSpectra the total K-characteristic peaks were in increasing order, as observed in the anode to cathode direction, whereas the Tucker model produced maXimum total K-characteristic peaks at the 6° anode side, and lesser amounts at the central aXis and the 6° cathode side. Large differences in the total K-characteristic lines is seen among the three different methods. The EGS4 code system was able to produce X-Ray Spectra for a combination of target materials.
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Diagnostic X‐Ray Spectra: A comparison of Spectra generated by different computational methods with a measured spectrum
Medical physics, 1998Co-Authors: Madhava Bhat, John E. Pattison, Giovanni Bibbo, Martin CaonAbstract:A number of computer codes, developed using semi-empirical models, are available to compute X-Ray Spectra from a tungsten target for different tube parameters. In this study X-Ray Spectra measured with a high-purity germanium detector are compared with those computed using the empirical models and previously published measured data. The computer codes used to generate the Spectra are based on models proposed by Birch et al. and Tucker et al. The measured X-Ray Spectra agreed well with the computed X-Ray Spectra using the model of Tucker et al. whereas the model of Birch et al. produced a “harder” X-Ray spectrum compared to the measured Spectra. Our measured X-Ray Spectra compared well with the previously published measured Spectral data of Fewell et al.
